In electronic devices such as personal digital assistants (PDA), laptop computers, OA devices, medical devices or car navigation and the like, a touch panel for providing an input means (i.e. a pointing device) in their displays has been widely used. It has been known that a representative touch panel adopts a capacitive type as well as a resistive type, an electromagnetic induction type, an optical type and the like.
In general, the capacitive type is divided into an analogue type and a digital type.
In the analogue type, a sensor electrode is an electrode in a sheet shape, and no pattern is required within a sensing operation area. On the contrary, the digital type needs a pattern of an electrode for a sensor within a sensing operation area. In this digital type, the capacitive touch panel adopts a variation in capacitance generated between a transparent electrode and electrostatics of the human body to induce currents which become a basis for confirming a touch position. To detect the position of a touch panel to which the human body such as fingers or a stylus is touched, various technologies for the capacitive touch panel have been developed.
As one example, U.S. Pat. No. 6,970,160 discloses a lattice touch-sensing system for detecting a position of a touch on a touch-sensitive surface. The lattice touch-sensing system may include two capacitive sensing layers, separated by an insulating material, where each layer consists of substantially parallel conducting elements, and the conducting elements of the two sensing layers are substantially orthogonal to each other. Each element may comprise a series of diamond shaped patches that are connected together with narrow conductive rectangular strips. Each conducting element of a given sensing layer is electrically connected at one or both ends to a lead line of a corresponding set of lead lines. A control circuit may also be included to provide an excitation signal to both sets of conducting elements through the corresponding sets of touch on the surface occurs, and to determine a position of the touch based on the position of the affected bars in each layer.
The capacitive type as described above is mainly composed of the configuration including two capacitive sensing layers. The two capacitive sensing layers are formed to have a space with an insulating material between the layers to bring about a capacitive effect between the layers. Due to this configuration, a structure of the panel becomes very thick, thereby going against a tendency for a small size in product. Moreover, the conventional capacitive touch panel includes a substrate on both surfaces in which two capacitive sensing layers are formed, respectively. In the light of this, through holes should be formed on the substrate so as to function as a bias. The circuit layering should be adopted to appropriately connect the conducting elements of the sensing layers. This makes a production of the capacitive touch panel difficult and complex.
Accordingly, to settle the problem, technologies for reducing two capacitive sensing layers to one capacitive sensing layer have been used.
FIG. 1 is a view illustrating an electrode pattern of a touch panel according to a conventional art. FIG. 2 is a cross-sectional view for explaining the electrode pattern of the touch panel according to the conventional art. The conventional touch panel and electrode pattern will be explained with reference to FIG. 1 and FIG. 2.
As illustrated in FIG. 1 and a on FIG. 2, on a substrate 110, a first-axis (Rx) capacitive pattern 120 is formed and second-axis (Tx) capacitive transparent pattern cells 131 are formed. These electrode patterns are illustrated as cross sections in FIG. 2.
At this time, as a method of forming the first-axis conductive pattern 120 and the second-axis conductive transparent pattern cells, an etching process, a sputtering process or a screen printing process may be used. Furthermore, as a material for the transparent pattern, indium-tin oxide (ITO) has been generally used.
Then, as illustrated in b on FIG. 2, a photo resist layer 10 is formed on the second-axis capacitive pattern cells 131, and thereafter, an insulating material is applied thereto, thereby forming a layer 40 to which the insulating material is applied.
Then, the photo resist 10 is removed, thereby forming an insulating layer 50 as illustrated in c on FIG. 2. On the insulating layer 50 formed like this, a bridge electrode 90 is formed, so the second-axis (Tx) conductive pattern cells 131 spaced apart from each other are electrically connected to each other.
However, because the conventional electrode pattern of the touch panel was problematic that the bridge electrode for connecting the conductive pattern cells 131 to each other is visible to the user's naked eye, a width of the bridge electrode was formed in 10 μm, but the problem in electric conductivity was generated. Accordingly, the bridge electrode was formed using a metal, but due to a difference in reflectance and color between the metal and an LCD around it, it was also problematic that the bridge electrode is visible to the naked eye.
Like this, to solve the problem in that the bridge electrode is visible to the naked eye, transparent materials such as ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), a carbon nano tube (CNT) and the like may be used. However, in this case, due to a cost problem for the materials and a limitation in conductivity of a transparent electrode, it is problematic that a design to reduce a width of the electrode cannot be made.